The present invention relates to devices for measuring the flowrate of fluids and in particular to such devices which incorporate a tapered flow tube within which is arranged a float.
It is known from published UK Patent Application No. 2111 196 A, for a flowmeter to include a glass tube with a tapered bore through which fluid, whose flowrate is to be measured, can flow. Arranged within the tube is a float which is so shaped that its position within the bore is dependent upon the flowrate of the fluid through the tube.
Radiation energy is directed across the path of movement of the float within the tube onto a tapered strip of photoconductive film on the glass tube surface behind the float. The electrical resistance of the film varies as a function of the position of the energy shadow incident on it due to the position of the float in the bore of the glass tube.
UK Pat. No. 807494 describes a device for sensing when the flowrate of a fluid within a pipe has dropped below a predetermined value. The device includes a vertical tapered tube for the passage therethrough of the fluid. A float is freely movable along the length of the tube. A photo-electric cell is arranged at or adjacent the bottom end of the tube so that ambient or other light entering the tube from the sides thereof will reflect from the lower half of the float towards the photo-electric cell.
When fluid flow through the tube lessens the float drops and at a predetermined cut-off point light is no longer reflected from the float in sufficient amount to operate the photo-electric cell and an alarm is actuated.
Medical equipment, for example, anaesthesia machines frequently require that the flowrate of two or more fluids be measured simultaneously and usually this is achieved by banks of flowmeters arranged side-by-side Flowmeters and sensing devices of the type described in UK Patent Application No. 2111 196 A and UK Pat. No. 807494 in which energy is radiated across the path of the movement of the float will either increase the overall width of the bank of flowmeters or obstruct vision of the float and tube.